Chidren celebrate as Nelson Mandela turns 93

School children sang Nelson Mandela a happy birthday on Monday (July 18), as the anti-apartheid icon turned 93.

Mandela -- known by his clan name of Madiba in South Africa -- has been receiving medical care at his home in Johannesburg's Houghton suburb since he was hospitalised at the start of the year, suffering from a respiratory disease.

He retired from public life in June 2004 before his 86th birthday, telling his compatriots: "Don't call me, I'll call you."

Since then he has rarely appeared in public and when he did, he appeared increasingly frail.

Mandela was treated in the 1980s for tuberculosis and later had an operation to repair damage to his eyes. In 2001 he had treatment for prostate cancer.

To celebrate his birthday, mandela's foundation urged people to give up 67 minutes of their time for charity work, to represent Mandela's 67 years of political activism.